# std::basic_filebuf

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< cpp‎ | io

Defined in header `<fstream>` |  |
template< class CharT, class Traits = std::char_traits<CharT> > class basic_filebuf : public std::basic_streambuf<CharT, Traits> |  |

`std::basic_filebuf` is a std::basic_streambuf whose associated character sequence is a file. Both the input sequence and the output sequence are associated with the same file, and a joint file position is maintained for both operations. The restrictions on reading and writing a sequence with `std::basic_filebuf` are the same as std::FILEs.

The functions underflow() and overflow() / sync() perform the actual I/O between the file and the get and put areas of the buffer. When `CharT` is not char, most implementations store multibyte characters in the file and a std::codecvt facet is used to perform wide/multibyte character conversion.

Several typedefs for common character types are provided:

Defined in header `<fstream>`
Type | Definition
`std::filebuf` | std::basic_filebuf<char>
`std::wfilebuf` | std::basic_filebuf<wchar_t>

### Member types

Type | Definition
`char_type` | `CharT`
`traits_type` | `Traits`; the program is ill-formed if `Traits::char_type` is not `CharT`.
`int_type` | `Traits::int_type`
`pos_type` | `Traits::pos_type` which is required to be std::fpos<Traits::state_type>
`off_type` | `Traits::off_type`
`native_handle_type`(C++26) | implementation-defined type that is TriviallyCopyable and `semiregular`

### Member functions

### Public member functions
(constructor) | constructs a `basic_filebuf` object (public member function)
operator= (C++11) | assigns a `basic_filebuf` object (public member function)
swap (C++11) | swaps two `basic_filebuf` objects (public member function)
native_handle (C++26) | returns the underlying implementation-defined handle (public member function)
(destructor) [virtual] | destructs a `basic_filebuf` object and closes the file if it is open (virtual public member function)
is_open | checks if the associated file is open (public member function)
open | opens a file and configures it as the associated character sequence (public member function)
close | flushes the put area buffer and closes the associated file (public member function)
### Protected member functions
showmanyc [virtual] | optionally provides the number of characters available for input from the file (virtual protected member function)
underflow [virtual] | reads from the associated file (virtual protected member function)
uflow [virtual] | reads from the associated file and advances the next pointer in the get area (virtual protected member function)
pbackfail [virtual] | backs out the input sequence to unget a character, not affecting the associated file (virtual protected member function)
overflow [virtual] | writes characters to the associated file from the put area (virtual protected member function)
setbuf [virtual] | provides user-supplied buffer or turns this filebuf unbuffered (virtual protected member function)
seekoff [virtual] | repositions the file position, using relative addressing (virtual protected member function)
seekpos [virtual] | repositions the file position, using absolute addressing (virtual protected member function)
sync [virtual] | writes characters to the associated file from the put area (virtual protected member function)
imbue [virtual] | changes the associated locale (virtual protected member function)

### Non-member functions

std::swap(std::basic_filebuf) (C++11) | specializes the std::swap algorithm (function template)

## Inherited from std::basic_streambuf

### Member types

Member type | Definition
`char_type` | `CharT`
`traits_type` | `Traits`; the program is ill-formed if `Traits::char_type` is not `CharT`.
`int_type` | `Traits::int_type`
`pos_type` | `Traits::pos_type`
`off_type` | `Traits::off_type`

### Member functions

(destructor) [virtual] | destructs the `basic_streambuf` object (virtual public member function of `std::basic_streambuf<CharT,Traits>`)
##### Locales
pubimbue | changes the associated locale and invokes imbue() (public member function of `std::basic_streambuf<CharT,Traits>`)
getloc | obtains a copy of the associated locale (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Positioning
pubsetbuf | invokes setbuf() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekoff | invokes seekoff() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekpos | invokes seekpos() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubsync | invokes sync() (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Get area
in_avail | obtains the number of characters immediately available in the get area (public member function of `std::basic_streambuf<CharT,Traits>`)
snextc | advances the input sequence, then reads one character without advancing again (public member function of `std::basic_streambuf<CharT,Traits>`)
sbumpcstossc (removed in C++17) | reads one character from the input sequence and advances the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sgetc | reads one character from the input sequence without advancing the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sgetn | invokes xsgetn() (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Put area
sputc | writes one character to the put area and advances the next pointer (public member function of `std::basic_streambuf<CharT,Traits>`)
sputn | invokes xsputn() (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Putback
sputbackc | puts one character back in the input sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sungetc | moves the next pointer in the input sequence back by one (public member function of `std::basic_streambuf<CharT,Traits>`)

### Protected member functions

(constructor) | constructs a `basic_streambuf` object (protected member function)
operator= (C++11) | replaces a `basic_streambuf` object (protected member function)
swap (C++11) | swaps two `basic_streambuf` objects (protected member function)
##### Locales
imbue [virtual] | reacts to a change of the associated locale (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
##### Positioning
setbuf [virtual] | replaces the buffer with user-defined array, if permitted (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
seekoff [virtual] | repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
seekpos [virtual] | repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
sync [virtual] | synchronizes the buffers with the associated character sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
##### Get area
showmanyc [virtual] | obtains the number of characters available for input in the associated input sequence, if known (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
underflow [virtual] | reads characters from the associated input sequence to the get area (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
uflow [virtual] | reads characters from the associated input sequence to the get area and advances the next pointer (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
xsgetn [virtual] | reads multiple characters from the input sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
ebackgptregptr | returns a pointer to the beginning, current character and the end of the get area (protected member function)
gbump | advances the next pointer in the input sequence (protected member function)
setg | repositions the beginning, next, and end pointers of the input sequence (protected member function)
##### Put area
xsputn [virtual] | writes multiple characters to the output sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
overflow [virtual] | writes characters to the associated output sequence from the put area (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
pbasepptrepptr | returns a pointer to the beginning, current character and the end of the put area (protected member function)
pbump | advances the next pointer of the output sequence (protected member function)
setp | repositions the beginning, next, and end pointers of the output sequence (protected member function)
##### Putback
pbackfail [virtual] | puts a character back into the input sequence, possibly modifying the input sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_fstream_native_handle` | `202306L` | (C++26) | native handles support

### See also

FILE | object type, capable of holding all information needed to control a C I/O stream (typedef)

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